no m/n or s/n available.......I'm stumped, this sys. hp was working fine until lastnight, now it's not working but fan and strips were running even when t-stat was removed...I replaced t-stat because display messed up and possible other issues....fan control board and fan reley....hp works now but fan and strips still continous...I checked wiring with sclematic, and it's correct....theres no low vt at reley until you raise temp above set point then theres vt and the reley makes contact , theres a slight pause in fan then hp comes on and fan comes back on.....nothing else to replace in the air handler....any ideas....